BT25Y钛合金在600 ℃—800 ℃的高温氧化行为研究

研究了BT25Y钛合金在600 ℃、700 ℃和800 ℃下的高温氧化行为。采用连续氧化增重法,并结合氧化速度常数、氧化活度等理论计算了合金的氧化动力学和热力学规律;利用XRD、SEM和EDS等表征方法研究了氧化膜的相结构和表面、截面形貌及元素分布。结果表明：BT25Y钛合金在600 ℃和700 ℃均有较好的抗氧化性能,其连续氧化动力学曲线符合抛物线规律,氧化层由细小TiO₂和Al₂O₃组成,氧化膜可有效阻止氧渗入基体,降低氧化速度;BT25Y钛合金在800 ℃氧化严重,其连续氧化动力学曲线近似符合直线规律,氧化层由Al₂O₃层和TiO₂层交替组成,氧化膜疏松多孔,不能有效阻挡氧向基体一侧的扩散。     

Si对625合金激光熔覆层高温氧化特性的影响

利用循环氧化法,研究了不同Si含量（0%,1%,3%,质量分数）的625合金熔覆层在700、800、900 ℃下氧化144 h后的高温氧化行为。用XRD分析了氧化物相。通过SEM/EDS研究了氧化物表面和截面的形貌、元素组成和氧化膜的厚度。结果表明,不同温度下试样的氧化动力学都保持抛物线规律,随着温度的升高,氧化增重逐渐增加。通过观察,在900 ℃时,0% Si含量的625合金熔覆层出现了氧化膜大面积剥落的情况,3% Si含量的合金熔覆层氧化膜保持完整。在700 ℃时,随着Si含量增加,氧化膜表面的氧化颗粒尺寸减小且更加致密,同时促进了Cr₂O₃氧化物的生成。在700 ℃下,0 % Si含量的试样出现了大片的内氧化区域;1% Si含量的试样基体部分出现了2处条状的含Ni,Cr,Mo的氧化物相区;而3% Si含量的试样氧化后由于生成了富Si的内氧化层,这阻止了内氧化的发生。外层Cr₂O₃氧化膜和内层SiO₂的联合作用既阻止了O阴离子的渗入也抑制了Fe等金属离子的扩散,提高了合金熔覆层的抗氧化性。     

空气反应钎焊ZrO2与GH3536接头组织与力学性能

采用Al₂TiO₅颗粒增强的Ag-CuO-Al₂TiO₅复合钎料,在钎焊温度为1050 ℃保温30 min工艺参数下,对ZrO₂陶瓷与GH3536合金进行了空气反应钎焊(RAB),分析了钎焊接头的界面结构及其形成机制;同时研究了接头在800 ℃氧化不同时间的组织演变规律及其对连接性能的影响。结果表明,钎焊过程中Al₂TiO₅颗粒分解产生Al₂O₃和TiO₂,TiO₂与ZrO₂陶瓷反应生成ZrTiO₄相。GH3536侧金属元素发生氧化形成尖晶石层,并分别与钎缝中的Al₂O₃、CuO反应,在钎缝中生成细密分布的NiAl₂O₄相及紧邻尖晶石层的团块状NiCuO₂相。ZrO₂/GH3536接头高温氧化1000 h后,钎缝中NiAl₂O₄呈团块状分布,Cr₂O₃薄层保持稳定;尖晶石层内部元素均匀化,厚度有明显增加。接头强度随着氧化时间的延长先降低后稳定在20 MPa。     

P92钢焊接接头的高温抗氧化性研究

P92钢因优异的综合性能逐渐成为超超临界机组过热器、再热器等零部件的理想用钢,材料经焊接后,焊接接头在服役温度中的高温抗氧化性直接影响零部件的使用寿命。利用增重法研究P92钢焊接接头在650℃高温空气介质中的氧化动力学,采用OM、SEM观察和分析氧化层表面及截面形貌,利用XRD分析氧化物物相。结果表明:在一定温度下,P92钢焊接接头各区域氧化速率均是先增加后降低,然后趋于稳定值,符合抛物线规律;在650℃空气介质中氧化132 h后,焊接接头中距焊缝3 mm热影响区A部位、焊缝、母材各区域氧化层的厚度分别为45μm,30μm,27μm;焊接接头氧化后表面的主要氧化产物为Fe_2O_3。     

等离子喷涂热障涂层高温 TGO 的形成与生长研究

目的研究热障涂层(TBC)和纯粘结层(BC)在1100℃下的氧化动力学,探讨热障涂层中热生长氧化物(TGO)组织结构的演化规律。方法运用大气等离子喷涂技术(APS)制备涂层,对比分析热障涂层和纯粘结层涂层在1100℃下等温氧化2,5,10,20,50,100,200,350 h后TGO的厚度变化,并对粘结层表面和热障涂层截面分别进行XRD和SEM分析。结果热障涂层和纯粘结层在1100℃下的氧化动力学均遵循抛物线规律,其氧化速率常数分别为0.344,0.354μm/h0.5。等温氧化5 h后,TGO的主要成分为α-Al2O3;随氧化时间的增加,生成Cr2O3、尖晶石、Co O和Ni O的混合氧化物;等温氧化100 h后,Co O消失,Ni O的含量减少,Cr2O3和尖晶石氧化物的含量增加;等温氧化350 h后,TGO中出现了裂纹,但涂层仍未剥落,TGO最终由顶层多孔的混合氧化物层和底层具有柱状晶结构的α-Al2O3层组成。结论顶层陶瓷层(TC)对热障涂层氧化速率常数的影响很小。TGO中α-Al2O3首先形成并以柱状结晶的方式生长,混合氧化物在α-Al2O3上形成,TGO生长速度逐渐变缓。     

电解TiO2中间相的形成与溢出气体间的关系

熔盐电解TiO₂制备金属钛的过程中,钙钛矿是不可避免的中间相,这已得到国内外研究者的公认。本研究借助间断性实验,主要研究了熔盐电解TiO₂制备金属钛过程中,钙钛矿的形成与TiO₂脱氧及阳极产生气体间的关系。研究结果表明,CaCl₂熔盐中电解TiO₂制备金属钛的过程,按其脱氧进程可分为三个主要阶段。第一阶段为 TiO₂脱氧生成钛的低价氧化物,同时O_2-、熔盐Ca₂₊和未脱氧的TiO₂形成CaTiO₃。第二阶段为CaTiO₃脱氧、脱钙及钛低价氧化物继续脱氧为Ti₂O。第三阶段为Ti₂O进一步脱氧为Ti(2% O)。TiO₂脱氧量、熔盐消耗量及形成CaTiO₃量之间的摩尔比为1:1:1, 且钙钛矿形成阶段阳极只有Cl₂放出,钙钛矿形成结束后阳极放出CO₂、CO气体,无Cl₂放出。若以电解TiO₂到含2%氧的Ti[O]所消耗的时间记为100%的话,那么钙钛矿脱氧、脱钙过程约占总时间的38.9%,而钙钛矿形成的时间只占5.6%,其余时间为钛低价氧化物的脱氧过程。因此钙钛矿的形成是该工艺电流效率低的主要原因之一,钛低价氧化物深脱氧速率低是该工艺的主要限制性环节。     

低氧分压下NiTi记忆合金氧化行为的研究

本文研究了NiTi形状记忆合金在H₂-H₂O气氛下400-700 °C的氧化行为。合金的氧化过程遵循立方规律,氧化激活能127.52 kJ/mol。氧化显著降低了试样表面的Ni含量。400 °C氧化的试样,其表面形貌与其他试样不同,并且氧化膜较薄,截面结构无法用SEM分析。500 °C、600 °C、700 °C氧化的试样,表面有两种形貌的氧化物,一种是颗粒状氧化物,另一种是晶须状氧化物。截面分析表明,氧化膜分为两层,上层由TiO₂构成,下层由Ni₃Ti构成,两层界面处有孔洞生成。     

高铬铸铁高温氧化产物转变和动力学研究

研究了高铬铸铁氧化动力学和不同氧化温度氧化产物生长形态、结构转变.结果发现:高铬铸铁组织中铁基体和合金碳化物表面生成的氧化物形核生长位置具有较强的选择性,500℃氧化,铁基体表面优先形核,氧化层结构由内层Cr2O3和外层针状Fe2O3组成,600℃以上氧化,氧化激活能增加,外层Fe2O3停止生长,氧化层结构转变为Cr2O3和颗粒状尖晶石型氧化物MnCrO4复合膜.分析了不同温度下氧化产物转变机理.     

Ti-6Al-4V合金高温氧化行为及显微组织研究

分析了Ti-6Al-4V合金在900 _oC,930 _oC,960 _oC温度下的氧化行为及表层显微组织变化。在0.5-24 h时间内,氧化层不断增厚,越靠近表面氧化层越疏松。氧含量在氧化层/富氧层界面的5 μm内发生急剧下降,进入富氧层后缓慢下降直到稳定。氧化层中以TiO₂为主,同时也出现了Al₂O₃。富氧层中的a相含量远远高于基体内部,其晶粒尺寸也发生长大。富氧层深度与热暴露时间的关系可用对数函数描述,通过线性回归分析计算出了O在富氧层中的扩散激活能为206 kJ/mol。     

Super 304H钢在700~900℃纯水蒸汽中的氧化行为

从氧化动力学、氧化膜相组成和微观结构方面,研究了两种表面状态的Super 304H钢在700~900℃纯水蒸汽中的氧化行为。结果表明:Super 304H钢的氧化动力学近似遵从抛物线规律,但是抛物线速率常数和氧化膜结构与氧化温度及试样表面状态密切相关。升高温度和抛光处理都显著增大了抛物线速率常数,促进了Fe氧化物瘤及其下方向内氧化区的生长。     

Oxidation of Mechanically Alloyed Al-rich Al–Ti Powders

The oxidation behavior of Al-rich, metastable mechanically alloyed powders in the Al–Ti binary system has been examined in the context of their potential application in high-energy-density materials. Scanning calorimetry and thermogravimetric analysis in an oxygen atmosphere up to 1500°C have been performed on powders, synthesized with compositions ranging from Al_0.95Ti_0.05 to Al_0.75Ti_0.25. Oxidation proceeds in three distinguishable steps, similar to the oxidation steps observed for pure aluminum. The steps become less pronounced with increasing Ti concentration. For both the first and second oxidation steps, the apparent activation energies are close to 400 kJ/mol. Partially oxidized material was recovered from intermediate temperatures for quantitative phase analysis by X-ray diffraction, Al₂O₃ and TiO₂ are the main oxidation products. Similarly to pure aluminum, metastable γ-alumina is present at temperatures below ∼ 1000°C, suggesting that the stepwise oxidation is related to phase transitions of the alumina in the oxide scale. At temperatures above 1300°C, oxidation follows melt formation in the binary Al–Ti system, as the aluminum component oxidizes selectively, leaving a titanium-rich metallic residue. No correlation was observed between the oxidation and melting of aluminum.     

Air Oxidation of Ni–Ti Alloys at 650–850°C

The oxidation of pure Ni and three Ni–Ti alloys containing 5, 10, and 15 wt.% Ti over the temperature range 650–850°C in air was studied to examine the effect of titanium on the oxidation resistance of pure nickel. Ni–5Ti is a single-phase solid solution, while the other two alloys consisted of nickel solid solution (-Ni) and TiNi₃. The oxidation of Ni–Ti alloys at 650°C follows an approximately parabolic rate law and produces a decrease in the oxidation rate of pure Ni by forming an almost pure TiO₂ scale. At higher temperatures, Ni–Ti alloys also follow an approximately parabolic oxidation, and their oxidation rates are close to or faster than those of pure Ni. Duplex scales containing NiO, NiTiO₃ and TiO₂ formed. Some internal oxides of titanium formed, especially at 850°C. In addition, the two-phase structure of Ni–10Ti and Ni–15Ti was transformed into a single-phase structure beneath the scales.     

Cyclic Oxidation Behavior of the Ti–6Al–4V Alloy

The cyclic oxidation behavior of the Ti–6Al–4V alloy has been studied under heating and cooling conditions within a temperature range from 550 to 850 °C in air for up to 12 cycles. The mass changes, phase, surface morphologies, cross-sectional morphologies and element distribution of the oxide scales after cyclic oxidation were investigated using electronic microbalance, X-ray diffractometry, scanning electron microscopy and energy dispersive spectroscopy. The results show that the rate of oxidation was close to zero at 550 °C, obeyed parabolic and linear law at 650 and 850 °C, respectively, while at 750 °C, parabolic—linear law dominated. The double oxide scales formed on surface of the Ti–6Al–4V alloy consisted of an inner layer of TiO₂ and an outer layer of Al₂O₃, and the thickness of oxide scales increased with an increasing oxidation temperature. At 750 and 850 °C, the cyclic oxidation resistance deteriorated owing to the formation of voids, cracks and the spallation of the oxide scales.     

Kinetics and Mechanism of the Oxidation of Molybdenum

The rates of formation of the different oxides on molybdenum in pure oxygen at 1 atm pressure have been determined in the temperature range 500° to 770°C. The rate of vaporization of MoOs is linear with time, and the energy of activation for its vaporization is 53,000 cal per mol below 650°C and 89,600 cal per mol at temperatures above 650°C. The ratio Mo0_{3(vaporizing)}/Mo0_3(surface) increases in a complicated manner with time and temperature. There is a maximum in the total rate of oxidation at 600°C. At temperatures below 600°C, an activation energy of 48,900 cal per mol for the formation of total Mo0₈ on molybdenum has been evaluated. The suboxide Mo0₂ does not increase beyond a very small critical thickness. At temperatures above 725°C, catastrophic oxidation of an autocatalytic nature was encountered. Pronounced pitting of the metal was found to occur in the temperature range 550° to 650°C. Marker movement experiments indicate that the oxides on molybdenum grow almost entirely by diffusion of oxygen anions.     

Nb/Mn/Si合金化的β-γ钛铝合金循环氧化行为（英文）

利用扫描电子显微镜、电子探针、电子背散射衍射和X射线衍射,研究Ti42Al1.5Mn3Nb0.1B合金和Ti42Al1.5Mn3Nb0.1B0.2C0.2Si合金在750～850℃下的循环氧化行为。两种合金的氧化增质曲线大致符合抛物线规律,且在800℃的氧化速率常数较Ti42Al5Mn1W合金的降低。在所有的实验温度下,两种合金表面都生成保护性良好的氧化膜,没有开裂或剥落发生。Nb的添加会抑制TiO₂的生长,促进Al的选择性氧化,使合金形成致密的Al₂O₃层。另外,微量Si元素的添加进一步提高合金的抗氧化性,使其生成更为致密的Al2O3层,在氧化过程中进一步抑制氧的内扩散,降低合金的氧化增质,且其效果在高温下更加明显。     

The Influence of the Rare Earth Element Ce on the High-Temperature Oxidation Kinetics of Low-Cr Steels

The oxidation behavior of steels containing low-Cr concentrations (0.5-2.25 wt.%) has been studied in laboratory air in the temperature range of 400-550 °C. The oxidation rate of the steels was lower than that of pure iron, but higher than that of pure iron when a small amount of rare earth element cerium (0.03 wt.%) is added to the 2.25Cr1Mo steel. The mass change follows a nearly parabolic law for the case of pure iron and the steel without Ce addition, while linear behavior describes the oxygen uptake for the case of the 2.25Cr1Mo+0.03Ce steel. SEM cross-section observations and thermodynamic calculations confirm that there is no wustite (FeO) formation during oxidation of pure iron and low-Cr steels at 550 °C, whereas FeO might be formed in the oxide scale of 2.25Cr1Mo+0.03Ce at the same oxidation conditions (temperature, atmosphere, and exposure time). By investigating the temperature for FeO stability, this study reveals that the temperature for FeO formation on pure iron is 568 °C, for the 2.25Cr1Mo steel 589 °C, and 471 °C for the 2.25Cr1Mo+0.03Ce. This low value for the FeO stability temperature found for the steel 2.25Cr1Mo+0.03Ce steel explains why this steel oxidizes very fast at 550 °C.     

Powder metallurgical processing of Ni–Ti–Zr alloys undergoing martensitic transformation: part I

Ni–Ti–Zr materials with Zr 12–25 at.% and Ni 42–50 at.% have been produced by powder metallurgy. Suitable temperatures for sintering in Ar-atmosphere Ni–Ti–Zr compacts are within the range 900–1000 °C. Sintering at temperatures above 1000 °C causes melting of the compacts with high Zr content. The presence of ZrC, ZrO₂, Zr₃O, TiO₂ and TiO of different modifications, complex oxides such as Ni₅TiO₇, Ti_0.5Zr_0.5O_0.2 and equilibrium phases after sintering at temperatures above 1000 °C in alloys with low Zr-content was derived from X-ray diffractometry. During sintering at temperatures below 1000 °C the phases belonging to the binary Ti–Ni and Ti–Zr systems were formed. Long-term sintering and slow furnace cooling allowed the precipitation of Ni₄Ti₃ and Ni₂Ti. The process of sintering is controlled by the diffusion of Ni in Ti and Zr particles during the early stages of sintering. Slow diffusion of Zr atoms in Ti₂Ni, Ti–Ni and diffusion of Ti atoms in Zr₂Ni, Ni–Zr controls the later stages of sintering.     

Isothermal oxidation behavior of powder metallurgy beta gamma TiAl–2Nb–2Mo alloy

A new TiAl–2Nb–2Mo beta gamma alloy was synthesized by powder metallurgy process. HIP’ed and vacuum heat treated specimens were isothermally oxidized at 800 °C and 900 °C in air up to 500 h. The TiAl–2Nb–2Mo alloy oxidized parabolically up to 500 h at both 800 °C and 900 °C. The oxides consisted of outer TiO₂ layer, intermediate Al₂O₃ layer, and inner TiO₂ rich mixed layer and the oxidation mechanisms of the alloy were identical at both temperatures. During oxidation, the degradation of lamellar colonies formed a diffusion zone just below the oxide/substrate interface consisting of γ-TiAl matrix and dispersed beta phases which contained high concentration of Nb and Mo. The oxidation rate of the TiAl–2Nb–2Mo alloy is more sensitive to temperature than those of the Ti–48Al–2Nb–2Cr and Ti–48Al–2Nb–2Cr–W alloys.